N
Nigel
There is no requirement for Zs to be of a value to operate the OCPD within the required time in the event of a fault to earth. The preferred means of earth fault protection on a TT is an RCD (411.5.2) and the maximum Zs value will be in accordance with table 41.5. (411.5.3).
The maximum value whether you like it or not is 1667 ohms for a 30ma RCD and that is the value to be recorded on a cert for a 30ma RCD.
Yeah that is what I said